Abstract
13 photons/cm2/sec (λmax 440, 470 and 600 nm). There was a distinct, but nonsignificant, difference in the phase shifting abilities of the light pulses with the 470 nm light being the most effective at phase advancing the Meloff50%. During the monochromatic light exposures the acute effects of light pulses on elevating core body temperature (07:15-07:45 h) and on subjective alertness (07:15-12:00 h) were also assessed. Alertness was monitored using a 9-point alertness scale (1 - very alert, 9 - very sleepy) and the Karolinska sleepiness. The high photon density 600 nm light condition was significantly less alerting than all other light conditions. When the data were normalised relative to the baseline value at 07:15 h, before the light exposure began, the 420 nm light pulse was significantly more alerting than the 470 nm light pulse (p = 0.05). When the mean alertness value during the entire light pulse was calculated a non-significant rank in the level of alertness was observed: high photon density 440 nm, low photon density 420 and 440 nm, 470 and 600 nm. The acute effects of light on core body temperature were also maximally responsive to the high photon density 440 nm light exposure. These data suggest short wavelength sensitivity of the acute effects of light. Although there were no statistically significant differences between the phase shifts observed with the different light conditions, the pattern of response suggests that 470 nm may be the most effective wavelength, of those tested, at phase advancing the melatonin rhythm. The acute effects of light on alertness and core body temperature appear to be most sensitive to 440 nm. This differential spectral sensitivity of the responses may reflect the use of different photoprocessing pathways. These preliminary results can be used as the basis for future research to determine the wavelength of maximal sensitivity which can then be used in practical situations to enhance circadian adaptation to shift work and new time zones.